1. Field of the Invention
The invention has to do with machine components having textured surfaces with controlled surface morphology which are prepared by means of electrochemical deposition. More particularly, the textured surfaces are comprised of peaks which have been electrochemically deposited on a substrate wherein the density, uniformity and size of the peaks is controlled by varying current density and other parameters in a pulsed direct current process.
2. The Related Art
Electrochemical methods of preparing textured surfaces have been described in the art. U.S. Pat. No. 5,185,073 to Bindra, et al., for example, describes the use of pulse electroplating and other methods for making dendritic surfaces. According to Bindra, the current is interrupted at a low frequency pulse rate on the order of 50 to 450 per second during the deposition. For example, palladium dendrite pulse plating was done at a peak current density of 500-1000 mA/cm2, a duty cycle of 10 to 20% and a pulse repetition rate of 200-417 per second. The reference, however, does not teach or suggest that peak characteristics can be controlled by a pulsed direct current process and it does not relate to dendritic surfaces of the type and composition which are deposited on machine components.
Pulse plating to make smooth surfaces is known, for example, a method to make nickel films is described in the May 1979 issue of Metal Finishing by Sun, et al., xe2x80x9cPlating With Pulsed and Periodic-Reverse Currentxe2x80x9d, pp. 33-38. The use of pulse plating to make hard smooth coatings of trivalent chromium is disclosed in U.S. Pat. No. 4,804,446 to Lashmore, et al. and U.S. Pat. No. 4,869,971 to Nee, et al. describes the use of pulse plating to make multi-layer smooth metallic surfaces. None of these pulse plating methodologies produce textured surfaces of the type made according to the present invention.
An electrochemical process for treating copper sheet or foil to produce an adherent nodularized surface, having a fine dendritic structure, which can be bonded to a non-metallic substrate is described in U.S. Pat. No. 4,468,293 and its divisional 4,515,671 to Polan, et al. According to Polan, the bath solution is maintained substantially at room temperature and pulses having a first current density from about 55 mA/cm2 to about 350 mA/cm2 followed by a second current density from about 5 mA/cm2 to about 50 mA/cm2 are employed. Polan""s frequency is from about 1 Hz to about 10,000 Hz and total deposition time is from about 2 seconds to about 60 seconds.
Electrochemical methods of depositing a structured surface layer on machine components are described in U.S. Pat. Nos. 5,415,761 and 5,958,207 to Mull but these methods require the use of complex ramping and stepwise waveforms.
The present invention provides a new method using a pulsed direct current process to electrochemically deposit, on an electrically conductive substrate, a textured surface having predictable peak characteristics. Typically, the substrate is a machine component such as a machine roll.
Machine components that require textured surfaces have various applications and they require various peak characteristics. Even within the same type of application, the required peak characteristics can vary substantially depending upon product needs and customer specifications. The present invention addresses these needs by providing a new methodology which enables those skilled in the art to customize the peak characteristics of a textured surface.
All percentages set forth herein are by weight/weight unless specifically denoted otherwise.
The improved textured surfaces of the invention can be deposited on various machine components such as machine rolls. The machine components having a textured surface made according to the invention can be used without further processing or they can be subjected to additional mechanical, chemical or electrochemical processes.
According to the invention, the desired density, uniformity and size of the peaks required for a textured surface are identified based on application requirements or customer specifications. The electrochemical parameters then are selected to make a surface texture having the requisite specifications. The parameters identified by the inventors herein have been found to have predictable effects on surface properties so that processing conditions can be identified with a minimum amount of experimentation. After the processing conditions have been identified, a machine component is immersed in a suitable electrodeposition bath. A charge having a first current density (it) is passed through the bath to the machine component and maintained for a first time interval (tt). The current density then is reduced to a second current density (ib) and maintained for a second time interval (tb). The current density then is increased to the first current density again and the cycle is repeated multiple times until the passage of a total deposition time (ttd). The first current density is greater than the second current density and the second current density is greater than zero.
The density, uniformity and size of the peaks is controlled according to the invention by varying the values of the parameters it, ib, tt, tb and ttd. The ratio of tt/tb also has an effect on peak characteristics. We have found that varying the value of it provides a coarse adjustment of peak characteristics and when the ratio of tt/tb is greater than 1, preferably from about 2:1 to about 6.5:1, especially about 2:1, variations in the values of tt and tb can provide a fine adjustment of peak characteristics. The relationship of each parameter to the surface characteristics of the end product is described in more detail below.
The temperature of the electrodeposition bath is maintained within the traditional operating range of the electrodeposition chemistry being plated, as is well known to those skilled in the art. When the process of the invention is applied to plating chrome, it is conducted at a bath temperature greater than 46xc2x0 C. and less than 60xc2x0 C. and preferably from about 47xc2x0 to about 55xc2x0 C.; most preferably from about 47xc2x0 to about 52xc2x0 C.